How do our bodies turn food into fuel?

So much goes on when we consume food. Once it enters our bodies, it gets broken down into tiny bits and pieces called macronutrients, or what we know as carbohydrates, protein and fats. These macronutrients are then processed and broken down even further, after which they are transported to various places in our bodies, where they play a variety of important roles that all help us function day in and day out. In this post, I’ll briefly go through how we turn the individual macronutrients into the fuel that supports our ever-hungry bodies.

Carbohydrates

There has always been a big misconception about carbs and how dangerous they apparently are. Well, carbohydrates are not dangerous, in fact, they are just like any other sources of energy – there are the healthy sources and less healthy sources. The fact is, that no matter what type of carbohydrate we consume our bodies will attempt to convert it into fuel for immediate or later use.

When a carbohydrate enters our bloodstream it will travel to wherever it is needed in the body. During this process, the body releases a hormone called insulin, which has the task of getting the carbohydrate from the blood and into the cells where they are converted into energy. Once the carbohydrate reaches, for example, a muscle cell, transporters known as GLUT4 help transport the carbohydrate into the cell and this is where the magic happens. Inside the cell, more specifically the mitochondria, the carbohydrate is run through what is known as the Citric Acid Cycle and converted into energy, which in physiological terms is known as ATP (Adenosine Triphosphate). Once the ATP molecule has been formed from what was once a carbohydrate, it will get sent to any place in the body that requires energy.

Now, this is where it gets tricky because if a carbohydrate isn’t needed for immediate energy it will get stored as something called glycogen, and this is where people start getting scared. We have glycogen stores in our liver and muscles, which we can utilize for energy during fast, explosive movements like sprints and weight training. If these glycogen stores a full, only then will the excess carbohydrates we consume get converted and stored as body fat for even later energy use, but only then. So actually, the carbohydrates we consume can go through TWO processes before it will get stored as body fat, which tells us that we really shouldn’t be that skeptical of this energy source. Some nutrient-dense sources of carbohydrates include oats, sweet potatoes/yams, fruits, quinoa, spelt, couscous etc. All you need to do is treat carbohydrates just like any other source of energy – anything in excess can be toxic to the body, but the right amounts can be very beneficial.

Protein

We need protein for a TON of important structures throughout the body, the most notable structures being our muscles. When our muscles get torn down during exercise, we need to recover somehow and this is where our good friend, protein, joins the conversation. When we consume sources of protein, it is broken down in a process called the protein synthesis. Basically, we need the protein synthesis to convert the protein we consume into strands of amino acids that we can utilize to build and repair the cells in our bodies. Once the strand of amino acids (protein) has been formed from the protein synthesis, it will get transferred into the bloodstream and wherever it is needed.

Just like with carbohydrates, though, protein is widely misunderstood too. The same people that believe that we should, by default, consume as little carbohydrates as possible also believe that we should be consuming as much protein as possible. They will go for anything that states “high protein” on the label because they believe that it is the healthiest choice. Unfortunately, the “high protein” sticker is just a cheap marketing trick that most corporations make use of these days and the matter of the fact is that protein is like anything else we consume – the amount we consume should match our activity level. If you are doing heavy weight-lifting exercises on a daily basis, you should definitely have a high protein intake (1-2g per pound of bodyweight). If most of your workouts consist of cardiovascular work like running, treadmill work, elliptical work etc., or minimal light-weight work 2-3 times a week it’s highly likely that you won’t even be needing 1g of protein per pound of bodyweight.

Personally, I have six fairly heavy weight-lifting sessions a week, and I typically consume a daily 200-220 grams of protein, which, for me, is about 1.3g of protein per pound of bodyweight.

Fat

Most of the fat we consume is better known as triglycerides, a molecule consisting of fatty acids. These triglycerides are digested and then packaged as lipoproteins in the liver, after which they will then get sent out into the bloodstream to be transported to whatever location they are needed. They either get transported to cells where they are needed for energy or stored in fat cells as body fat if there is an excess intake.

To get better at turning triglycerides stored as body fat into fuel, some people resort to a ketogenic diet. A ketogenic diet is a diet consisting of a high fat intake and low-carb intake, which aims to force the body to burn fat instead of carbohydrates for its main source of energy. To understand how this works, it is important to note that the brain and the central nervous system mainly uses carbohydrates as its main fuel because carbohydrates can cross the blood-brain barrier, whereas fatty acids can’t. So, after a few days of high-fat/low-carb consumption, the body realizes that it needs an alternative energy source for its central nervous system and therefore begins to produce what is known as ketone bodies from the triglycerides stored in our fat cells. Once we achieve a high enough concentration of ketone bodies in our blood, these ketone bodies can then be used by our body’s tissues as a source of energy.

A way to mimic the benefits of a ketogenic diet without necessarily having to switch to a high-fat/low-carb diet is to combine your current preferred way of eating with a time-restricted feeding (TRF) diet. A TRF diet doesn’t require you to restrict your carbohydrate intake but instead requires you to restrict the amount of time you spend eating throughout the course of a day, prompting you to fast for a period of your day. Once we begin fasting, we can temporarily force our bodies to go into a ketogenic, fat-burning state for a short period of time, relying on the production of ketone bodies for energy.

If you want to know more about how time-restricted feeding and other types of fasting works, check out my previous post on the subject here…